Host complement system and innate immune factors

The host complement system and innate immune factors represent a complex network of proteins and cellular components that serve as the first line of defense against pathogens (StatPearls, 2023). The complement system consists of over 30 plasma and cell-surface proteins that interact in a regulated cascade to promote opsonization, inflammation, and direct lysis of microbes (Janeway's Immunobiology, 2017). Innate immune factors include pattern recognition receptors (PRRs), cytokines, and antimicrobial peptides that coordinate the immediate response to infection (NIH, 2022). Dysregulation of these systems is implicated in various pathologies, including paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and severe inflammatory responses such as those seen in COVID-19 (Nature Reviews Immunology, 2020). Therapeutic targeting of specific components, such as C3 (e.g., pegcetacoplan) or C5 (e.g., eculizumab), aims to modulate excessive immune activation while maintaining essential host defense mechanisms (FDA, 2021). These interventions are critical for managing diseases where the complement system causes collateral tissue damage (PubMed, 2022). However, inhibiting these factors requires careful monitoring due to the increased risk of infections by encapsulated bacteria (StatPearls, 2023).

Other names

Complement systemInnate immune systemComplement cascadeInnate immunity

Therapeutic agents target specific components of the complement cascade (e.g., C1s, C3, C5, Factor D, Factor B, or C5a receptors) to inhibit pathway activation, prevent the formation of the membrane attack complex (MAC), or block the pro-inflammatory effects of anaphylatoxins.